Inaccurately accounted scatter from the radioemission activity that is outside of the field of view (FOV) is one of the major sources of errors in quantitative PET imaging. If the outside-FOV activity was not accounted for properly, deviations on the order of 10% of the reconstructed emission activity can be introduced into the reconstructed image.
One way to account for outside-FOV activity is to perform an additional PET/CT scan of adjacent regions. In clinical practice this may be undesirable due to time limitations and other factors such as possibly increased radiation dose to the patient, e.g. if a computed tomography (CT) scan is employed in the extension to adjacent regions.
In clinical practice, the problem of outside-FOV activity is sometimes ignored, or is addressed by making some assumptions about the outside-FOV activity. In one such latter approach, if there is an activity in the first and last visible slices, then extension (duplication) of those slices can be performed to extend the volume by a certain empirically established distance. The correction for the scatter contamination can then be derived from such assumptions. The accuracy of the approach depends upon the extent to which the assumption(s) are justified. In another approach, the maximum extrapolation of the outside-FOV activity is limited by the length of the object as well as the scanned axial extent distance. This approach works well for uniform cylinder phantoms of various lengths when the cylinder phantom is positioned centered with respect to the center of the axial FOV, but may be less accurate in most other (clinical) cases.
The following discloses a new and improved systems and methods that address the above referenced issues, and others.